Optical displacement measuring device

ABSTRACT

An optical displacement measurement apparatus increasing the valid light receiving area struck by light so as to give a larger signal and reducing the effect of any unevenness or spottiness of the illuminance of the light source or any scratches or dirt on the glass scale is provided. The apparatus has a plurality of light receiving element arrays having a plurality of light receiving elements, has a plurality of light receiving element groups having a plurality of light receiving element arrays, has the plurality of light receiving element arrays arranged shifted by predetermined distances in the direction of movement of the glass scale, and has the light receiving element groups arranged shifted by predetermined distances with respect to the direction of movement of the glass scale. At this time, it is possible to make the width of the valid light receiving portions larger than the width of the invalid light receiving portions, provide one or more light receiving element arrays having a plurality of light receiving elements, and provide a plurality of light receiving element groups having a plurality of light receiving element arrays.

TECHNICAL FIELD

The present invention relates to an optical displacement measurementapparatus, more particularly relates to a high precision opticaldisplacement measurement apparatus using a photoelectric transmissiontype linear encoder, used for a contact type digital displacement meter.

BACKGROUND ART

In the past, optical measurement devices using lasers or light emittingdiodes (LED) and optical measurement devices using optical encoders havebeen known. Optical measurement devices can achieve a high precisionsince they use as units of measurement the wavelengths of the lasers orLEDs. Further, optical measurement devices are mainly used for measuringthe length between two points, i.e., measuring relative position.Optical encoder measurement devices are comprised of a scale made of aglass plate, film, metal sheet, etc., an optical grid provided at apredetermined pitch from the scale, a fixed index grid arranged facingthe scale across a predetermined distance (the phase of the optical gridand the phase of the fixed index grid being shifted 90 degrees), a fixedlight source for emitting parallel light to the scale, and a lightreceiving sensor. When the scale moves, the optical grid and fixed indexgrid overlap with each other to produce differences in lightness areproduced. The light receiving sensor detects the difference inlightness. Optical encoder measurement devices are being usedcommercially as digital displacement meters and are mainly being usedfor measuring the length between two points, i.e., measuring relativeposition.

Below, optical encoder measurement devices of the prior art will beexplained with reference to the drawings.

FIG. 1 shows the state of use of a contact type digital displacementmeter 40 including a photoelectric transmission type linear encoder. Thecontact type digital displacement meter 40 is used connected to acounter 41 by a connection cable 7. The contact type digitaldisplacement meter 40 is supplied with power from the counter 41 toperform measurement and outputs the measurement value to the counter 41.The counter 41 processes the signal output from the contact type digitaldisplacement meter 40 and digitally displays the obtained measurementvalue on a display unit 42. Therefore, the displacement of an objectmeasured by the contact type digital displacement meter 40 is displayedon the display unit 42 as a digital value.

The contact type digital displacement meter 40 has a frame 8 covered byan upper cover 9A and a lower cover 9B and has bearings 18 fastened atthe two ends of the frame 8. The bearings 18 support a spindle 5. Acontactor 6 is screwed into the front end of the spindle 5.

When measuring the length, thickness, etc., the contactor 6 screwed intothe front end of the spindle 5 is brought into contact with the measuredobject. Displacement of the measured object causes the spindle 5 to movein the arrow direction. The displacement of the spindle 5 is detected bythe photoelectric transmission type linear encoder built into thecontact type digital displacement meter 40, the detection output isprocessed by the counter 41, and the displacement of the measured objectis displayed on the display unit 42.

FIG. 2 explains the principle of a conventional photoelectrictransmission type linear encoder built into the contact type digitaldisplacement meter 40 explained in FIG. 1. The spindle 5 into which thecontactor 6 is screwed has connected to it a moving scale 3 made of atransparent member. The moving scale 3 is formed with an equal pitchoptical grid 11.

At one side of the moving scale 3 are provided a light source 1 and acondenser lens 2. At the other side are provided a fixed scale 34 formedwith equal pitch optical grids 47 and 48 and light receiving elements,i.e., photodiodes 28. The light source 1 and the photodiodes 28 faceeach other across the moving scale 3 moving in accordance withdisplacement of the measured object and the fixed scale 34 fixed to aconstant position.

The optical grid 11 provided at the moving scale 3 and the optical grids47 and 48 provided at the fixed scale 34 have the same pitches and sameline widths, for example, pitches of 20 μm and line widths of 10 μm. Thetwo types of scales are fabricated to extremely high precisions.

At the time of measurement, the spindle 5 moves in the arrow direction.The amount of light passing through the scales becomes maximum when thetransparent portions of the optical grid 11 of the moving scale 3 andthe transparent portions of the optical grids 47 and 48 of the fixedscale 34 match. On the other hand, when the moving scale 3 moves byexactly ½ of the pitch of the optical grid from that state, thetransparent portions and nontransparent portions of the optical gridsoverlap, so the amount of light transmitted becomes the minimum. Thatis, along with movement of the moving scale 3, the signals output fromthe photodiodes 28 become sinusoidal signals. By counting the number oftheir cycles, the distance of movement of the moving scale 3 can befound.

In general, the fixed scale 34 is normally provided with two opticalgrids 47 and 48. Corresponding to this, two photodiodes 28 are alsoprovided. Further, one optical grid 47 is shifted by exactly ¼ pitchfrom the other optical grid 48.

FIG. 3 shows the signals output from the two photodiodes 28 when themoving scale 3 moves. If expressing the light passing through oneoptical grid 47 of the fixed scale 34 as the signal A in FIG. 3, thesignal B expressing the light passing through the other optical grid 48of the fixed scale 34 is shifted in phase from the pitch P of the signalA by ¼ pitch. It is possible to determine the right or left direction ofmovement of the moving scale 3 by the advance or delay of the phase ofthe signal B with respect to the signal A.

FIG. 4 shows the configuration of a first prior art of a photoelectrictransmission type linear encoder built into the contact type digitaldisplacement meter 40 explained in FIG. 1. A cross-section of the linearencoder is shown. The linear encoder is mainly provided with two LEDs 1used as light sources, a moving scale 3, a spindle 5, a fixed scale 34,and two photodiodes 28.

The frame 8 has an upper cover 29A and lower cover 29B and a linearencoder support base 30 screwed to it. The spindle 5 is supported by twobearings 18 fastened to the frame 8. A contactor 6 for contacting themeasured object is screwed into the front end of the spindle 5. Themoving scale 3 is positioned with and fastened to a moving scale supportbase 31. The moving scale support base 31 is positioned with andfastened to the spindle 5, so movement of the spindle 5 becomes movementof the moving scale 3. The moving scale 3 is sandwiched between thelight source LEDs 1 and condenser lenses 2 and the light receiving sidefixed scale 34 and photodiodes 28.

For a stopping mechanism of the spindle 5, while not shown, a stoppingrod is fastened to the spindle 5 at one end. The other end slides in agroove provided in the frame 8 to thereby function as a stop. Further,the rod is linked with the frame 8 by a tension spring and is set toapply a suitable contact pressure to the measured object.

At the light emitting side, the two LEDs 1 are fastened to the LEDsupport base 32. The condenser lenses 2 are fastened to the LEDs 1. TheLED support base 32 is positioned with and screwed to the linear encodersupport base 30 so as to facilitate positioning with the light receivingside. The two LEDs 1 and condenser lenses 2 sandwich the moving scale 3between them and face the light receiving side fixed scale 34 and twophotodiodes 28.

At the light receiving side, the two photodiodes 28 are set on a PCB(printed circuit board) 33. The PCB 33 is fastened to the linear encodersupport base 30. The fixed scale 34 is set on the linear encoder supportbase 30 between the photodiodes 28 and the moving scale 3. Two sets ofgradations are cut into it. As with the explanation of the principle inFIG. 2, the pitches and line widths of the two optical grids 47 and 48provided at the fixed scale 34 are exactly the same as the optical grid11 of the moving scale 3, but the gradations are shifted in relativeposition by exactly ¼ pitch corresponding to the two photodiodes 28.

When the spindle 5 moves and the moving scale 3 is moved due tomeasurement, the light from the LEDs 1 and condenser lenses 2 passesthrough optical grid 11 of the moving scale 3 to produce differences inlightness. When the transparent portions of the optical grid 11 matchwith the transparent portions of the optical grids 47 and 48 of thefixed scale 34, the light is bright, while when they are shifted inphase by 180°, the light becomes dark. The repetition of the differencesin lightness of the light is detected by the photodiodes 28. As shown inFIG. 3, two sinusoidal signals A and B having the same period and havinga 90 degree phase difference are output from the photodiodes 28 by the ¼pitch shifted optical grids 47 and 48 of the fixed scale 3. Thesesignals A and B are amplified and digitalized, then electrically dividedand output as 1 μm pulses to enable measurement of the length.

FIG. 5 is a view of the configuration of a photoelectric transmissiontype linear encoder of a second prior art. The photoelectrictransmission type linear encoder shown in FIG. 5 is comprised of a glassscale 10 (moving scale 3 of first prior art), an optical grid 11provided on the glass scale 10, a light source 1 for emitting parallellight to the glass scale 10, fixed index grids 51 to 54 for receivinglight passing through the glass scale 10, an index base 50 on which thefixed index grids 51 to 54 are provided, light receiving elements 61 to64 for receiving the light passing through the fixed index grids 51 to54, and a board 20 on which the light receiving elements 61 to 64 areprovided. Further, the board 20 is provided with a semiconductorintegrated circuit (IC) 22 and a terminal 21 for connecting with a cable7C.

Note that the phases of the fixed index grids 51 to 54 are shifted in 90degree increments with respect to the optical grid 11. Further, thelight receiving elements 61 to 64 are comprised of single lightreceiving elements such as photosensors. The signals obtained areconverted to length using the prior art of “interpolation” forconverting voltage to distance.

FIG. 6 is a view of the configuration of an optical transmission typelinear encoder of a third prior art. The optical transmission typelinear encoder shown in FIG. 6 is comprised of a glass scale 10, anoptical grid 11 provided on the glass scale 10, a light source 1 foremitting parallel light to the glass scale 11, a light receiving elementarray 37 for receiving the light passing through the glass scale 10, anda board 20 on which the light receiving element array 37 is provided.Further, the board 20 is provided with a semiconductor integratedcircuit (IC) 23 and a terminal 21 for connecting with a cable 70.

FIG. 7 will be used to explain the configuration of the opticaltransmission type linear encoder of the third prior art in furtherdetail. The light receiving element array 37 is comprised of a pluralityof light receiving elements. P shows the pitch of the light receivingelements, u shows the width of the valid light receiving portion 35, andr shows the width of the invalid light receiving portion. Here, P is setto S×3/4, u to S/2, and r to S/4. That is, the ratio of u and r is 2:1.

Therefore, four light receiving elements g1, g2, g3, and g4 are providedcorresponding to the three optical grids e1, e2, and e3. Further, thelight receiving elements are configured so as to give the same amount oflight for every four elements. Further, the phases of the four lightreceiving elements g1, g2, g3, and g4 are shifted by 90° increments.Therefore, lines are laid for each four light receiving elements and thevalues added. Here, the total of the added outputs from the valid lightreceiving portions a1, a2, a3 . . . of the light receiving elements 37is designated as A, the total of the added outputs from the valid lightreceiving portions b1, b2, b3 . . . of the light receiving elements 37as B, the total of the added outputs from the valid light receivingportions c1, c2, c3 . . . of the light receiving elements 37 as C, andthe total of the added outputs from the valid light receiving portionsd1, d2, d3 . . . of the light receiving elements 37 as D. This being so,the phases of the added output signals A, B, C, and D are shifted by 90degree increments. The optical transmission type linear encoder of thethird prior art measures length by processing the output signals A, B,C, and D. These output signals A to D are changed to length using theconventional interpolation technique.

In the above first prior art, however, since the difference in lightnessdue to the overlap of the moving scale 3 and the fixed scale 34 wasdetected by photodiodes 4, the fixed scale 34 was essential, the contacttype digital displacement meter 40 could not be made thin, and thereforethe contact type digital displacement meter 40 became large in size.Further, the distance between the moving scale 3 and the fixed scale 34had to be made a narrow 10 to 50 μm, therefore there was the problemthat adjustment for positioning the surfaces of two scales with eachother was extremely difficult.

Further, the photoelectric transmission type linear encoder of thesecond prior art was comprised by a combination of the glass scale 10,fixed index grids 51 to 54 corresponding to the fixed scale 34 in thefirst prior art, and light receiving elements 61 to 64. The fixed indexgrids 51 to 54 were essential, so the contact type digital displacementmeter 40 became large in size. Further, to perform measurement with ahigh precision, it was necessary to accurately set the distance betweenthe index grids, the pitch of the fixed index grids 51 to 54, the ratioof transparent portions and nontransparent portions of the fixed indexgrids 51 to 54, the distance between the glass scale 10 and the fixedindex grids 51 to 54, and the distance between the fixed index grids 51to 54 and the light receiving elements 61 to 64.

Further, the light receiving elements 61 to 64 were comprised of singlelight receiving elements such as photosensors, so it was difficult toarrange them close to each other, a wide area was occupied, and theefficiency of use of the portion which the light struck was lowered.

On the other hand, in the third prior art, the size of the lightreceiving elements had to be fixed to S×3/4 and the width r of theinvalid light receiving portions was set to S/4. It was not possible tofurther lower this.

Further, as problems common to the second and third prior arts, therewere the problems of how to widen the valid light receiving portions ofthe light receiving elements to raise efficiency at the portion struckby light and what measures to take when the illuminance of the lightsource was spotty or when the glass scale was scratched or dirty.

That is, if the areas of the valid light receiving portions of the lightreceiving elements are small at the portion struck by the light, theoutputs become smaller, there is susceptibility to noise, and there is adetrimental effect on the measurement precision. Further, when theilluminance of the light source is uneven or spotty, the same lightreceiving sensor always gave values different from the normal values andthere was a detrimental effect on the measurement precision. Further,when the glass scale 10 was scratched or dirty, the location ofdifferences in illuminance would move along with movement of the glassscale, the light receiving elements receiving this would give erroneousvalues, and there would therefore be a detrimental effect on themeasurement precision.

DISCLOSURE OF INVENTION

Therefore, a first object of the present invention is to provide acontact type digital displacement meter which eliminates the fixed scalefor detecting the difference in lightness of an overlapping moving scaleand fixed scale, makes the contact type digital displacement meterthinner, and facilitates adjustment for positioning the surfaces of twoscales with each other.

A second object of the present invention is to enable the effects of anyunevenness or spottiness of the illuminance of the light source or anyscratches or dirt on the glass scale to be suppressed and prevent adetrimental effect on the measurement precision of an opticaldisplacement measurement apparatus.

A third object of the present invention is to increase the areas of thevalid light receiving portions of the light receiving elements at theportion struck by the light from the light source so as to raise thelight receiving efficiency and to enable the effects of any unevennessor spottiness of the illuminance of the light source or any scratches ordirt on the glass scale to be suppressed and prevent a detrimentaleffect on the measurement precision of an optical displacementmeasurement apparatus.

To achieve the first object, in the case of an optical displacementmeasurement apparatus having a displaceable first member having anoptical grid, a light source for emitting light to the first member, anda light receiving element unit for receiving light passing through thefirst member, the present invention is characterized by setting adistance between the first member and light receiving element units to ½of a Talbot distance and comprising the light receiving element unit bylight receiving element groups. Further, in the case of a photoelectrictransmission type linear encoder comprised of a light source comprisedof an LED and condenser lens, a first member comprised of a movingscale, and a photodiode masked at the same pitch as the first member,the present invention is characterized by setting a distance between thefirst member and the photodiode to ½ of a Talbot distance.

Here, the “Talbot” phenomenon is the phenomenon that the samedistribution of light intensity is reproduced as on the surface of acyclical structure at a distance (Talbot distance) of a whole multipleof the distance given by

Zt=(2×D ²)/λ

where D is the grid pitch and λ is the wavelength, when emitting planarmonochromatic light to a cyclical structure such as a diffraction gridand was discovered by H. F. Talbot in 1836.

According to this means, if the pitch of the moving scale is made 20 μmand the wavelength λ of the light emitting element is made 700 nm, thedistance forming a Talbot image becomes

(2×D ²)/λ=Zt=1,142 μm

Therefore, it is sufficient to set a light receiving element, that is, aphotodiode, at a position of Zt/2=571 μm. Compared with the past, thedistance can be increased 10 to 500 fold, the ease of assembly can beimproved, and an inexpensive contact-type digital displacement meter canbe provided.

To achieve the second object, an optical displacement measurementapparatus of the present invention is an optical displacementmeasurement apparatus having a displaceable first member having anoptical grid, a light source for emitting light to the first member, anda light receiving element unit for receiving light passing through thefirst member, characterized in that the light receiving element unit iscomprised of light receiving element groups which are arranged shiftedin increments of a predetermined distance with respect to a direction ofdisplacement of the first member.

In this case, it is possible to configure the light receiving elementgroups by providing a plurality of light receiving element arraysprovided at a predetermined pitch of the valid light receiving portionsand the invalid light receiving portions. Further, it is possible toarrange the plurality of light receiving element arrays shifted byincrements of a predetermined distance in the direction of displacementof the first member. The optical grid may be comprised of transparentportions and nontransparent portions provided at a pitch S of a ratio ofthe width of the transparent portions and the width of thenontransparent portions of 1:1. Further, the light receiving elementscomprising the light receiving element arrays may be provided at a pitchS of a width of the valid light receiving portions and a width of theinvalid light receiving portions of 1:1.

According to this configuration, since there are a plurality of lightreceiving elements having specific positional information and there area plurality of dispersed light receiving element arrays comprised of aplurality of light receiving elements having this specific positionalinformation, even when the illuminance of the light source is uneven orspotty or when the glass scale is scratched or dirty, all of the lightreceiving elements suffer that effect a bit each and average it out andtherefore it is possible to prevent any detrimental effect on themeasurement precision.

To achieve the third object, the optical displacement measurementapparatus of the present invention has a displaceable first memberhaving an optical grid, a light source for emitting light to the firstmember, and light receiving element arrays for receiving light passingthrough the first member and having a plurality of light receivingelements at the valid light receiving portions and invalid lightreceiving portions, characterized in that the pitch of the optical gridis larger than the pitch of the light receiving elements and the lightreceiving element arrays are arranged in the direction of displacementof the first member.

In this case, it is possible to make the ratio of the width of thetransparent portions and the width of the nontransparent portions of theoptical grid of the first member 1:1 and make the width of the validlight receiving portions and width of the invalid light receivingportions of the light receiving elements such that the width of thevalid light receiving portions is larger than the width of the invalidlight receiving portions.

In addition, it is possible to make the width of the invalid lightreceiving portions 2 to 3 μm.

Further, it is possible to provide light receiving element groups havingpluralities of light receiving element arrays.

According to this configuration, since the width of the valid lightreceiving portions and width of the invalid light receiving portions ofthe light receiving elements are such that the width of the valid lightreceiving portions is larger than the width of the invalid lightreceiving portions, it is possible to increase the areas of the validlight receiving portions of the light receiving elements at the portionstruck by light and possible to give resistance to noise and prevent adetrimental effect on the measurement precision.

Further, since a plurality of light receiving elements having specificpositional information are arranged dispersed or a plurality of arrayscomprised of a plurality of dispersed light receiving elements havingspecific positional information are arranged dispersed, even when theilluminance of the light source is uneven or spotty or when the glassscale is scratched or dirty, all of the light receiving elements of thepositional information suffer that effect a bit and average it out andtherefore it is possible to prevent any detrimental effect on themeasurement precision.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features, advantages, etc. of the presentinvention will be explained in detail below according to embodimentsshown in the attached drawings, in which:

FIG. 1 is a view of the overall configuration showing the state of useof a contact type digital displacement meter to which the presentinvention is applied.

FIG. 2 shows a first prior art and explains the principle of aphotoelectric transmission type linear encoder of a contact type digitaldisplacement meter.

FIG. 3 is a waveform diagram of waveforms of the signals output from thephotodiodes of FIG. 2.

FIG. 4 is a sectional view of the configuration of an example of aconventional photoelectric transmission type linear encoder.

FIG. 5 is a view of the configuration of a photoelectric transmissiontype linear encoder of a second prior art.

FIG. 6 is a view of the configuration of a photoelectric transmissiontype linear encoder of a third prior art.

FIG. 7 is a view of the relationship between an optical grid and lightreceiving element array in the third prior art.

FIG. 8 is a view explaining the principle of the optical displacementmeasurement apparatus of the present invention.

FIG. 9 is a sectional view of a contact type digital displacement meterof the first embodiment of the present invention.

FIG. 10 is an enlarged view of the light receiving surface of a maskedphotodiode of FIG. 9.

FIG. 11 is a further enlarged view of part of the light receivingsurface of FIG. 10.

FIG. 12 is a schematic view of the configuration of an opticaldisplacement measurement apparatus to which second to fourth embodimentsof the present invention are applied.

FIG. 13 shows the second embodiment of the present invention and is anenlarged view of a predetermined light receiving element group of FIG.12.

FIG. 14 is a view of the relationship between an optical grid and lightreceiving element array.

FIG. 15 shows the second embodiment of the present invention and is anenlarged view of another light receiving element group of FIG. 12.

FIG. 16 is a view of the arrangement of light receiving element groupsaccording to the second embodiment.

FIG. 17 is a view of changes of signals obtained from light receivingelements of the second embodiment and a 10th embodiment.

FIG. 18 is a view of the arrangement of light receiving element groupsaccording to a third embodiment.

FIG. 19 is a view of the arrangement of light receiving element groupsaccording to a fourth embodiment.

FIG. 20 is a view of the relationship between an optical grid and lightreceiving element groups according to the fourth embodiment.

FIG. 21 is a schematic view of the configuration of an opticaldisplacement measurement apparatus according to fifth to 10thembodiments of the present invention.

FIG. 22 is a view of the relationship between an optical grid and lightreceiving element groups according to a fifth embodiment.

FIG. 23 is a comparative view of a light receiving element array of aconventional configuration emitting a signal every 1 μm the same as inthe present invention.

FIG. 24 is a view of an optical grid and light receiving element groupsaccording to a sixth embodiment.

FIG. 25 is a view of an optical grid and light receiving element groupsaccording to a seventh embodiment.

FIG. 26 is a view of an optical grid and light receiving element groupsaccording to an eighth embodiment.

FIG. 27 is a view of an optical grid and light receiving element groupsaccording to a ninth embodiment.

FIG. 28 is a view of an optical grid and light receiving element groupsaccording to a 10th embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 8 is a view explaining the principle of the optical displacementmeasurement apparatus of the present invention. In the figure, 1 is alight source, 2 a condenser lens, 3 a moving scale, 4 a masked lightreceiving element, that is, a photodiode, 5 a spindle, 6 a contactor,and 11 an optical grid marked on the moving scale 3. In this figure, anLED is used for the light source 1, while the optical grid 11 iscomprised of bars having a predetermined line width and predeterminedlength and blocking light and marked on the moving scale 3 at apredetermined pitch. The LED 1 and the photodiode 4 are arranged facingeach other across the moving scale 3 which moves in accordance withdisplacement. The moving scale 3 is provided with a spindle 5 projectingfrom it. At the front end of the spindle 5 is screwed a contactor 6 forcontacting the measured object.

The light receiving surface of the photodiode is given two maskings. Thepitches and line widths of the maskings are similar to those of theoptical grid 11 of the moving scale 3, but the two maskings are shiftedfrom each other by ¼ pitch. The distance between the moving scale 3 andthe photodiode 4 is set to the value Zt/2 of half of the Talbot distanceZt.

When planar monochromatic light strikes the moving scale 3, the Talbotdistance Zt is given by Zt=(2×D²)/λ where D is the scale pitch and λ isthe wavelength. The same distribution of light intensity as the movingscale 3 is reproduced at that position. Further, the distribution oflight intensity of the moving scale 3 shifted by ½ cycle is reproducedat the position of half of that distance.

In actuality, the LED 1 does not emit completely planar monochromaticlight, so the distribution of light intensity of the moving scale 3 canbe reproduced and a clear image obtained at a short distance of zt/2 ofhalf of the Talbot distance Zt.

When bringing the contactor 6 into contact with the measured object andmeasuring the movement of the measured object, the spindle 5 moves inthe direction shown by the arrow along with displacement of the measuredobject. In this case, when the bright portions of the Talbot image ofthe moving scale 3 formed on the light receiving surface of the maskedphotodiode 4 match with the not masked portions of the light receivingsurface, the amount of light received by the photodiode 4 becomesmaximum. When the Talbot image moves by exactly ½ of the pitch from thisposition, the amount of light received becomes minimum. Further, thephotodiode 4 has two light receiving parts shifted by ¼ pitch, so thetwo signals output from the masked photodiode 4 become sinusoidalsignals shifted by ¼ pitch. By counting the number of cycles of thesignals, the distance of movement of the moving scale and, from thephase difference of the signals, the left or right direction ofmovement, can be found.

Next, embodiments of the present invention will be explained using thedrawings. The contact type digital displacement meter 40 incorporatingthe photoelectric transmission type linear encoder of the presentinvention is also used, as explained in FIG. 1, connected to a counter41 by a connection cable 7. The value measured by the contact typedigital displacement meter 40 is displayed on a display unit 42 of thecounter 41.

FIG. 9 shows a first embodiment of the present invention and shows across-section of the contact type digital displacement meter 40incorporating the photoelectric transmission type linear encoderexplained in FIG. 1. The frame 8 has an upper cover 9A, lower cover 9B,and linear encoder support base 17 screwed to it. A spindle 5 issupported by two bearings 18 fastened to the frame 8. A contactor 6screwed into the front end of the spindle 5 contacts the measuredobject. The moving scale 3 is positioned with and fastened to a movingscale support base 19, while the moving scale support base 19 ispositioned with and fastened to the spindle 5, so movement of thespindle 5 becomes the same as movement of the moving scale 3. The movingscale 3 is sandwiched between an LED 1 provided with a condenser lens atthe light emitting side and a masked photodiode 4 at the light receivingside.

For the stopping mechanism of the spindle 5, while not shown, one end ofa stopping rod is fastened to the spindle 5. The other end slides in agroove provided in the frame 8 to thereby function as a stopping member.Further, the rod is linked with the frame 8 by a tension spring and isset to apply a suitable contact pressure to the measured object.

At the light emitting side, the LED 1 to which the condenser lens 2 isfastened is fastened to the LED support base 14 screwed to the frame 8and faces the masked photodiode 4 at the light receiving side across themoving scale 3. The LED support base 14 is positioned by being screwedinto the linear encoder support base 17 so as to facilitate positioningwith the light receiving side. The masked photodiode 4 at the lightreceiving side is positioned with and fastened to the PCB 15 and issupported by a photodiode protective member 16 of substantially the sameheight as the photodiode 4.

FIG. 10 shows an embodiment of a mask directly printed on the photodiode4 by photolithography. The light receiving surface 43 of the maskedphotodiode 4 is divided into a first masking part 44 and a secondmasking part 45. The first masking part 44 and the second masking part45 are masked by lines of the same pitch and same line width as theoptical grid 11 of the moving scale 3. Further, the first masking part44 and second masking part 45 are arranged shifted by ¼ pitch in thesame way as the fixed scale 34 of the prior art (FIG. 2) anddiscriminate whether the moving scale 3 has moved to the left or right.

FIG. 11 is a further enlargement of the L part of FIG. 10. The lightreceiving part 43 of the photodiode matches with the pitch of theoptical grid 11 of the moving scale 3 and has a line width setsubstantially equal as well. In the present embodiment, when the pitchof the moving scale is 20 μm and the line width is 10 μm, one pixel 46of the light receiving part has a pitch of 20 μm and a line width of 8μm. The length is 36 μm.

Here, returning to FIG. 9, the operation of the contact type digitaldisplacement meter 40 will be explained. The light emitted from the LED1 passes through the condenser lens 2 and the moving scale 3 and forms aTalbot image at a predetermined position from the moving scale 3 basedon the wavelength of the LED 1 and the pitch of the moving scale 3. Thatis, if the pitch of the moving scale is 20 μm and the wavelength of theLED 1 is 700 nm, it is formed at a position of zt/2=2×20²/0.7/2=571 μmfrom the moving scale 3. Therefore, by setting the masked photodiode 4at this position, the Talbot image of the moving scale 3 is formed atthe light receiving part 43 of the photodiode 4.

When the bright portions of the Talbot image of the moving scale 3 andthe light receiving pixels 46 at the light receiving unit 43 of thephotodiode 4 match, the sinusoidal signal output from the photodiode 4becomes maximum, while when the dark portions and the light receivingpixels 46 match, the sinusoidal signal output becomes the minimum.

As explained in FIG. 10, the light receiving part 43 has a first maskingpart 44 and a second masking part 45 shifted by ¼ pitch, so, asexplained in FIG. 3, the signal A is obtained from the first maskingpart 44 and the signal B from the second masking part 45 and it ispossible to determine the left or right direction of movement of themoving scale 3.

As explained above, according to the present invention, the distancebetween the masked photodiode 4 and the moving scale 3 can be set to 570μm by making it the Talbot distance zt/2. Since the distance can beenlarged 10 to 500 times from that of the past, the assembly andadjustment of distance become extremely easy, the fixed scale isunnecessary, and the cost can be reduced.

As clear from the above explanation as well, the masked photodiode 4 mayalso be an aggregate of pixels of CCDs. If the pitch is the same as themoving scale, it is sufficient to set two CCDs shifted by ¼ pitch.

FIG. 12 shows the configuration of a photoelectric transmission typelinear encoder to which the second to fourth embodiments of the presentinvention are applied and shows one embodiment of the internalconfiguration of the contact type digital displacement meter 40explained in FIG. 1. Reference numeral 10 is a glass scale serving asthe moving scale. A light blocking optical grid 11 of a length E isprovided on it. The glass scale 10 is connected to a spindle 5 shown inFIG. 1 and moves in the A-B direction by displacement of the measuredobject. Reference numeral 1 is a light source for emitting parallellight to the glass scale 10.

Reference numeral 200 is an aggregate of light receiving element groupsfor receiving light passing through the glass scale 10 provided on aboard 20 and corresponds to the photosensor 4 explained in FIG. 8. Theaggregate 200 of light receiving element groups is comprised of lightreceiving element groups 201 to 204. Reference numeral 22 is asemiconductor integrated circuit for position processing (IC chip),while 21 is a terminal for connecting with a cable 70. The cable 70supplies power to the circuits on the board 20. Further, the signalsfrom the circuits on the board 20 are transmitted by the cable 70 to adisplay device or other external device.

FIG. 13 shows a second embodiment of the present invention. The figureenlarges one light receiving element group 201 in the aggregate 200 oflight receiving element groups to show details of the same. The lightreceiving element group 201 is comprised of eight light receivingelement arrays 331 to 338 arranged in parallel with the direction ofmovement A-B of the glass scale 10. The light receiving element arrays331 to 338 are comprised of pluralities of light receiving elements 39.

Here, the relationship between the light receiving elements 39 at thelight receiving element arrays 331 to 338 and the optical grid 11 at theglass scale 10 will be explained using FIG. 14. FIG. 14 is an enlargedview of part of the optical grid 11 and light receiving element array331 and shows the dimensional relationship among the parts. The arrowA-B shows the direction of movement of the glass scale 10. S shows thepitch of the optical grid 11, W shows the width of a transparent portion12 of the optical grid 11, and V shows the width of a nontransparentportion 13 of the optical grid 11. Here, the width w of the transparentportion 12 and the width V of the nontransparent portion 13 are set to ½of the pitch S of the optical grid 11. For example, if the pitch S ofthe optical grid 11 of the glass scale 10 is set to 8 μm, the width W ofthe transparent portion 12 of the optical grid 11 is 4 μm and the widthV of the nontransparent portion 13 of the optical grid 11 is 4 μm.

On the other hand, each of the plurality of light receiving elements 39comprising the light receiving element array 331 is comprised of a validlight receiving portion 35 able to receive light and an invalid lightreceiving portion 36 not able to receive light. P shows the width of alight receiving element 39, u the width of the valid light receivingportion 35, and r the width of the invalid light receiving portion.Here, the width P is equal to the pitch S of the optical grid 11, whilethe width u of the valid light receiving portion 35 and the width r ofthe invalid light receiving portion are set to ½ of the pitch S of theoptical grid 11.

As will be understood from FIG. 13, the light receiving element arrays331 to 338 are all comprised of the same dimensions. Each of the lightreceiving element arrays 331 to 338 is comprised of 100 light receivingelements 39 arranged in the lateral direction (direction parallel toA-B) and one light receiving element 39 in the longitudinal direction(direction perpendicular to A-B).

The pitch P of each light receiving element 39 is set to 8 μm in thesame way as the pitch S of the optical grid 11. Further, the valid lightreceiving portions u and invalid light receiving portions r are set to 4μm each in the same way as the transparent portions 12 andnontransparent portions 13 of the optical grid 11. Therefore, the lengthLx of each light receiving element array in the lateral directionbecomes 800 μm (8 μm×100). Further, the length g of each light receivingelement 39 in the longitudinal direction is set to 100 μm, so the totallength LLy of eight light receiving element arrays 331 to 338 in thelongitudinal direction is 800 μm.

Further, in the second embodiment, the adjoining light receiving elementarrays are arranged shifted in the lateral direction from each other byexactly ⅛ of the pitch S of the optical grid 11, that is, the distancef=S/8=1 μm. Therefore, the total length LLx of the light receivingelement array group 201 in the lateral direction becomes the length Lxof one light receiving element array in the lateral direction plus seventimes the shift distance f, that is, a length of 807 μm. Note that here,the light receiving element arrays are arranged shifted by 1 μmincrements in the A direction with respect to the light receivingelement array 331 at the top in the figure, but if necessary the amountof shift f may also be made f=S×n (n is an integer)+S/8. Further, thelight receiving element arrays 331 to 338, as shown in FIG. 13, werearranged in contact with each other without clearance, but it is alsopossible to arrange the light receiving element arrays 331 to 338 whileproviding a space between the adjoining arrays.

FIG. 15 is a view of details of another light receiving element group202 in the aggregate 200 of light receiving element groups. The lightreceiving element group 202 is comprised of seven adjoining lightreceiving element arrays 337 to 331 arranged parallel to the directionof movement A-B of the glass scale 10 shifted by 1 μm increments in theB direction with respect to the light receiving element array 338 at thetop of the figure. The light receiving element group 202 differs fromthe light receiving element group 201 in only the point that thedirection of shift of the adjoining light receiving element arrays withrespect to the light receiving element array at the top of the figure isopposite. The size of the light receiving elements 39 and the pitch andnumber of the light receiving element arrays are the same as those ofthe light receiving element group 201.

Therefore, if the total length LLx of the light receiving element arraygroup 202 in the lateral direction is 807 μm and the adjoining lightreceiving element arrays are shifted by 1 μm increments in the Bdirection of the direction of movement A-B of the glass scale 10 withrespect to the light receiving element array 338 at the top of thefigure, the position of the light receiving element array 331 at thebottom in the direction of movement of the glass scale 10 becomes thesame as that of the light receiving element array 331 of the lightreceiving element array group 201. Thus, the numbers from the lightreceiving element arrays 331 to 338 in the light receiving element arraygroup 202 of FIG. 15 are assigned corresponding to the light receivingelement arrays emitting the same signals as the light receiving elementarrays 331 to 338 of the light receiving element group 201 in FIG. 14due to movement of the glass scale 10.

FIG. 16 shows the overall configuration of the aggregate 200 of lightreceiving element groups in the second embodiment. The light receivingelement group 201 and the light receiving element group 202 wereexplained using FIG. 13 and FIG. 15, but the light receiving elementgroup 203 is a light receiving element group the same as the lightreceiving element group 202, while the light receiving element group 204is a light receiving element group the same as the light receivingelement group 201. The distance C between the light receiving elementgroup 201 and the light receiving element group 202 may be any distance.Further, in the light receiving element arrays emitting the same signalsin the light receiving element groups 201 to 204, only the position ofthe light receiving element array 331 is shown.

The light receiving element arrays 331 of the light receiving elementgroup 201 and the light receiving element group 202 are arranged in thesame positional relationships relative to the transparent portions 12and nontransparent portions 13 of the glass scale 10. The lightreceiving element arrays 331 of the light receiving element group 203and light receiving element group 204 are also arranged in the samepositional relationships relative to the transparent portions 12 andnontransparent portions 13 of the glass scale 10. Further, the lightreceiving element arrays 331 of the light receiving element group 201and light receiving element group 203 are arranged at locations of wholemultiples of the pitch S of the glass scale 10 in positionalrelationship.

For this reason, these four light receiving element arrays 331 are allarranged at the same positional relationships relative to thetransparent portions 12 and nontransparent portions 13 of the glassscale 10. Due to this, the same signal is generated from these fourlight receiving element array 331. This will be explained using FIG. 16.

The light receiving element arrays 331 of the light receiving elementgroup 201 and the light receiving element group 202 have head positionsstarting from the same position. The light receiving element arrays 331of the light receiving element group 203 and the light receiving elementgroup 204 similarly have head positions starting from the samepositions. Further, the positional relationship between the lightreceiving element arrays 331 is such that the total length LLy of thelight receiving element array 331 of the light receiving element group201 is 800 μm and the distance d from the end of the light receivingelement array 331 of the light receiving element group 201 to the headof the light receiving element array 331 of the light receiving elementgroup 203 is a whole multiple of the pitch S of the optical grid 11(when whole number is n, S×n). That is, the head positions of all of thelight receiving element arrays 331 are positions of whole multiples ofthe pitch =8 μm of the glass scale 10 and the same signal is producedfrom these four light receiving element arrays 331 due to movement ofthe glass scale 10.

For the remaining light receiving element arrays 331 to 338 as well, thesame signals are generated from the light receiving element arrays ofthe same numbers due to movement of the glass scale 10 in view of thepositional relationship with the light receiving element array 331. Thatis, it is understood that there are four dispersed light receivingelement arrays from which the same signals are produced due to movementof the glass scale 10.

Due to this, in the second embodiment, it is understood that there are aplurality of light receiving elements having specific positionalinformation and there are a plurality of dispersed light receivingelement arrays comprised of pluralities of light receiving elementshaving such specific positional information. Therefore, when theilluminance of the light source is uneven or spotty or when the glassscale 10 is scratched or dirty, the effect is suffered a bit by all ofthe light receiving elements of the positional information and averagedout so it is possible to prevent any detrimental effect on themeasurement precision.

Next, the flow of the signals output from the light receiving elementgroups 201 to 204 will be explained taking as an example the lightreceiving element arrays 331. Assume that the glass scale 10 and thelight receiving element arrays 331 are in the positional relationshipshown in FIG. 14. That is, assume that the transparent portions 12 ofthe glass scale 10 and the valid light receiving portions 35 of thelight receiving elements 39 match and that the nontransparent portions13 of the glass scale 10 and the invalid light receiving portions 36 ofthe light receiving elements 39 match. At this time, the signalsobtained from the light receiving elements 39 become maximum. Thesignals from the four light receiving element arrays 31 obtained byadding all of these also become maximum.

When the glass scale 10 moves in the A direction, the nontransparentportions 13 of the glass scale 10 gradually cover the valid lightreceiving portions 35 of the light receiving elements 39. As a result,the outputs of the light receiving elements 39 gradually become smaller.When the optical grid 11 moves by exactly ¼ of the pitch S, the outputsof the light receiving elements 39 become ½ of the maximum output, whilewhen it moves by exactly ½ of the pitch S, the valid light receivingportions 35 are completely covered by the nontransparent portions 13, sothe outputs of the light receiving elements 39 become the minimumoutput. When the glass scale 10 moves further and moves by ¾ of thepitch S, the outputs of the light receiving elements 39 return to ½ ofthe maximum output. When moving by exactly one pitch S, the maximumoutputs are again obtained from the light receiving elements 39.

The same is true for the other light receiving element arrays 332 to338. On the other hand, the light receiving element arrays 332 to 338are positioned shifted by 1 μm increments with respect to the lightreceiving element array 331, so the outputs of the light receivingelements 39 become maximum 1 μm delayed with respect to the lightreceiving element array 331. This relationship is shown by the waveformsI31 to I38 in FIG. 17. In the figure, I31 is the output signal of thelight receiving element array 331, while I32 to I38 correspond to thelight receiving element arrays 332 to 338.

If converting the signals I31 to I38 to digital values using acomparator having a threshold value of (maximum output−minimumoutput)/2, the results are the digital signals J31 to J38. Here, thedigital signal SJ31 is the signal I31 converted to a digital value andinverts at (maximum output−minimum output)/2. The digital signals J32 toJ38 correspond to the signals I32 to I38.

Further, the digital signals J31 to J38 are converted to two signals KAand KB comprised of

KA=J31·J37+J33·J35

KB=J32·J38+J34·J36

by a logical operation circuit. The timings of the signals KA and KB areshown in FIG. 17 as well. As will be understood from FIG. 17, one cycleof the signal I31 is equal to the pitch S (=8 μm) of the optical grid 11of the glass scale 10, so the distance from the rising edge or thetrailing edge of the signal KA to the trailing edge or rising edge ofthe signal KB becomes exactly 1 μm.

Therefore, if counting the number of the rising edges or trailing edgesof the signals KA and KB, the result is eight pitches S (cycles) of theoptical grid 11. By displaying these, it is possible to measure thedistance of movement of the optical grid 11, that is, the glass scale10. Further, for differentiating the direction of movement of the glassscale 10, if taking note of the rising edge of the signal KB, when theglass scale 10 moves in the A direction, the signal KA becomes “1”,while when the direction of movement is B, it becomes “0”, sodifferentiation is possible.

FIG. 18 shows a third embodiment of the present invention and shows theoverall configuration of an aggregate 200′ of the light receivingelement groups. The aggregate 200′ of light receiving element groups iscomprised of the light receiving element groups 201′ to 204′. Thepositional relationships of the light source 1, glass scale 10, andboard 20 are similar to those of FIG. 12.

The configuration of the light receiving element array group 201′ in theaggregate 200′ of light receiving element groups is the same as that ofthe light receiving element array group 201 in the aggregate 200 oflight receiving element groups of the first embodiment explained in FIG.16. Further, the configurations of the other light receiving elementarray groups 202′ to 204′ in the aggregate 200′ of the light receivingelement groups are exactly the same as that of the light receivingelement array group 201′. Further, these four light receiving elementgroups are arranged shifted relative to each other by a set distance.The distance C between the light receiving element group 201 and thelight receiving element group 202 may be any distance.

In FIG. 18, the explanation will be given taking note of only the lightreceiving element array 331 in the light receiving element group 201′.The light receiving element array 331 is the array shown by the numeral1 in the light receiving element group 201′ (hereinafter referred to asthe “first array”). After this, similarly, the light receiving elementarrays 332 to 338 are referred to as the second array to the eightharray. The light receiving element group 202′ is arranged shifted in theA direction of the direction of movement A-B of the glass scale byexactly 2 μm from the light receiving element array 201′. The first toeighth arrays of the light receiving element group 201′ are arrangedshifted by 1 μm increments in the A direction of the direction ofmovement A-B of the glass scale. Further, the pitch S of the opticalgrid 11 of the glass scale is 8 μm.

Thus, among the first to eighth arrays of the light receiving elementgroup 202′, the one at the same position relative to the glass scale 10as the first array of the light receiving element group 201′ is theseventh array. That is, the first array of the light receiving elementgroup 201′ and the seventh array of the light receiving element group202′ emit the same signal by the movement of the glass scale 10. Thus,the seventh array of the light receiving element group 202′ correspondsto the light receiving element array 331.

Similarly, the arrays of the light receiving element group 201′ andlight receiving element group 202′ correspond to each other on a 1 to 1basis in all numbers as shown below. That is, the first array to sixtharray of the light receiving element group 202′ correspond to the thirdarray to eighth array of the light receiving element group 201′, whilethe seventh array and eighth array of the light receiving element group202′ correspond to the first array and second array of the lightreceiving element group 201′.

Next, the first array of the light receiving element group 203′ isarranged at a position of a whole multiple of the pitch S (=8 μm) of theoptical grid 11 plus 4 μm with respect to the first array of the lightreceiving element group 201′. In FIG. 18, LLy+d corresponds to this.Since LLy=800 μm and d=8×n (n is a whole number)+4 μm, this can beconfirmed.

By arranging them in this way, the array at the same position relativeto the optical grid 11 of the glass scale 10 as the first array of thelight receiving element group 201′ is the fifth array. This is becausethe first array of the light receiving element group 203′ is shifted by4 μm from a whole multiple of the pitch S of the optical grid 11 and thefifth array is further shifted by 4 μm from the first array. Thus, thesame signal is output from the first array of the light receivingelement group 201′ and the fifth array of the light receiving elementgroup 203′, so the fifth array corresponds to the light receivingelement array 331.

Similarly, the arrays of the light receiving element group 201′ and thelight receiving element group 203′ correspond 1 to 1 in all numbers asshown below. That is, the first array to fourth array of the lightreceiving element group 201′ correspond to the fifth array to eightharray of the light receiving element group 203′, while the fifth arrayto eighth array of the light receiving element group 201′ correspond tothe first array to fourth array of the light receiving element group203′.

Further, the first array of the light receiving element group 204′ isarranged at a position shifted in the A direction of the direction ofmovement A-B of the glass scale 10 by exactly 2 μm with respect to thefirst array of the light receiving element group 203′. Therefore, thefirst array of the light receiving element group 204′ is arranged at aposition of a whole multiple of 8 μm plus 6 μm with respect to the firstarray of the light receiving element group 201′.

By arranging them in this way, the array at the same position relativeto the optical grid 11 of the glass scale 10 as the first array of thelight receiving element group 201′ is the third array. This is becausethe first array of the light receiving element group 204′ is shifted by6 μm from the whole multiple of the pitch S of the optical grid 11,while the third array is shifted by a further 2 μm from the first array.Thus, the same signal is emitted from the first array of the lightreceiving element group 201′ and the third array of the light receivingelement group 204′, so the third array corresponds to the lightreceiving element array 331.

Similarly, the arrays of the light receiving element groups 201′ andlight receiving element group 204′ correspond 1 to 1 in all numbers asshown below. That is, the first array to sixth array of the lightreceiving element group 201′ correspond to the third array to eightharray of the light receiving element group 204′, while the seventh arrayand eighth array of the light receiving element group 201′ correspond tothe first array and second array of the light receiving element group204′.

Thus, due to movement of the glass scale 10, taking note of the lightreceiving element arrays 331 from which the same signal is output, thefirst array in the light receiving element group 201′, the seventh arrayin the light receiving element group 202′, the fifth array in the lightreceiving element group 203′, and the third array in the light receivingelement group 204′ correspond to the light receiving element arrays 331.Thus, it is understood that the light receiving element arrays 331 arearranged dispersed among the four light receiving element groups 201′ to204′.

It is understood that the remaining light receiving element arrays 332to 338 are dispersed in the same way as the light receiving elementarrays 331. That is, it is understood that there are four dispersedlight receiving element arrays generating the same signal.

From this, in this embodiment as well, it is understood that there are aplurality of light receiving elements having specific positionalinformation and there are a plurality of dispersed light receivingelement arrays comprised of pluralities of light receiving elementshaving that specific positional information. Therefore, when theilluminance of the light source is uneven or spotty or when the glassscale 10 is scratched or dirty, the effect is suffered a bit by all ofthe light receiving elements of the positional information and averagedout, so it is possible to prevent any detrimental effect on themeasurement precision.

The processing of the signals obtained from the aggregate 200 of thelight receiving element groups of the third embodiment shown in FIG. 18is similar to the mode explained in FIG. 16, so its explanation will beomitted.

FIGS. 19 and 20 show a fourth embodiment of the present invention. Thepositional relationships of the light source 1, glass scale 10, andboard 20 are the same as in the configuration explained in FIG. 12. Inthe fourth embodiment, however, as shown in FIG. 20, the aggregate 200of the light receiving element groups is changed to the aggregate 200′of the light receiving element groups.

In the second and third embodiments of the present invention, the lightreceiving element arrays 331 to 338 in the light receiving elementgroups 201 to 204 and 201′ to 204′ were arranged adjoining in thedirection perpendicular to the direction of movement of the glass scale10, while the adjoining light receiving element arrays 331 to 338 werearranged shifted in the direction of movement of the glass scale 10 by 1μm increments.

On the other hand, in the fourth embodiment of the present invention, asshown in FIG. 20, the four light receiving element groups 201″ to 204″are arranged in parallel at spaces of a predetermined distance C in thedirection of movement of the glass scale 10. Further, the lightreceiving element groups 201″ to 204″ are comprised of light receivingelement arrays 331 to 338, the light receiving element arrays 331 to 338are arranged in the direction perpendicular to the direction of movementof the glass scale, and spaces of 1 μm are provided between theadjoining light receiving element arrays.

The light receiving element arrays 331 to 338, as shown in FIG. 19, arecomprised of pluralities of light receiving elements 39. Each lightreceiving element 39 is comprised of a valid light receiving portion 35able to receive light and an invalid light receiving portion 36 not ableto receive light. P shows the width of the light receiving elements 39,u shows the width of the valid light receiving portion 35, and r showsthe width of the invalid light receiving portion. Here, the width P ofthe light receiving element 39 is set to the pitch S of the optical grid11, while the width u of the valid light receiving portion 35 and thewidth r of the invalid light receiving portion are set to S/2,respectively.

As will be understood from FIG. 19, the eight light receiving elementarrays 331 to 338 are all comprised of the same dimensions. Each of thelight receiving element arrays 331 to 338 is comprised of 25 lightreceiving elements 39 arranged in the lateral direction (directionparallel to A-B) (for convenience in illustration, only three of thelight receiving elements 39 are drawn by broken lines) and one lightreceiving element 39 in the longitudinal direction (directionperpendicular to A-B).

The pitch P of each light receiving element 39 is set to 8 μm in thesame way as the pitch S of the optical grid 11. Further, the width u ofthe valid light receiving portion and the width r of the invalid lightreceiving portion are set to 4 μm in the same way as the transparentportions 12 and nontransparent portions 13 of the optical grid 11.Therefore, the length Lx of one light receiving element array in thelateral direction becomes 200 μm (8 μm×25). Further, the total lengthLLx of each light receiving element group is 1607 μm (8 μm×200+7 μm).Further, the length q of each light receiving element is set to 400 μm,so the length Ly of each of the light receiving element arrays 331 to338 is also 400 μm.

Here, the light receiving element array 331 at the left end of the glassscale 10 in the direction of movement B in the light receiving elementgroup 201″ is placed in the same positional relationship relative to thetransparent portions 12 and nontransparent portions 13 of the glassscale 10. If doing this, the light receiving element array 331 has thesame relationship with the light receiving element array 331 shown inthe second and third embodiments.

The second light receiving element array from the left in the lightreceiving element group 201″ is shifted by 1 μm with respect to thelight receiving element array 331. This results in the same relationshipwith the light receiving element array 332 shown in the secondembodiment. Similarly, the third array from the left in the lightreceiving element group 201″, corresponds to the light receiving elementarray 333, the fourth array from the left the light receiving elementarray 334, etc. The light receiving element array at the right endcorresponds to the light receiving element array 338.

The light receiving element group 202″ is arranged in the directionperpendicular to the direction of movement of the glass scale 10 andshifted by 2 μm in the A direction of the direction of movement A-B ofthe glass scale 10. The light receiving element group 203″ is similarlyarranged shifted by 2 μm with respect to the light receiving elementgroup 202″, while the light receiving element group 204″ is similarlyarranged shifted by 2 μm with respect to the light receiving elementgroup 203″. These four light receiving element group 201″, lightreceiving element group 202″, light receiving element group 203″, andlight receiving element group 204″ are exactly the same inconfiguration, but differ in positions relative to the glass scale 10.

Now, take note of the light receiving element array 331 in the lightreceiving element group 201″. The light receiving element array of thelight receiving element group 202″ at the same position relative to theglass scale 10 as the light receiving element array 331 of the lightreceiving element group 201″ is the seventh light receiving elementarray. This corresponds to the light receiving element array 331.Similarly, the light receiving element array 331 of the light receivingelement group 201″ corresponds to the seventh light receiving elementarray of the light receiving element group 203″ and the third lightreceiving element array of the light receiving element group 204″.

The remaining light receiving element arrays 332 to 338 of the lightreceiving element group 201″ also correspond to some numbers of lightreceiving element arrays of the light receiving element group 202″ tolight receiving element group 204″.

Therefore, the light receiving element arrays 331 outputting the samesignals due to movement of the glass scale 10 become the first array inthe light receiving element group 201″, the seventh array in the lightreceiving element group 202″, the fifth array in the light receivingelement group 203″, and the third array in the light receiving elementgroup 204″. It is understood that other light receiving element arrays332 to 338 outputting the same signals are similarly dispersed. That is,it is understood that light receiving element arrays outputting the samesignals are dispersed at four locations of the light receiving elementgroups 201″ to 204″.

From this, in this embodiment as well, it is understood that there are aplurality of light receiving elements having specific positionalinformation and there are a plurality of dispersed light receivingelement arrays comprised of pluralities of light receiving elementshaving that specific positional information. Therefore, when theilluminance of the light source is uneven or spotty or when the glassscale 10 is scratched or dirty, the effect is suffered a bit by all ofthe light receiving elements of the positional information and averagedout, so it is possible to prevent any detrimental effect on themeasurement precision.

The processing of the signals output from the aggregate 200″ of thelight receiving element groups is similar to the second and thirdembodiments, so its explanation will be omitted.

In the second to fourth embodiments, the example was shown of four lightreceiving element groups, but the number of the light receiving elementgroups is not limited to four. Any number is possible if the light isdispersed from a light source which is not normal. Further, the distanceof shifting the light receiving element groups and the distance ofshifting the light receiving element arrays are of course also notlimited to the above values so long as similar effects to the aboveembodiments are obtained.

In this way, according to the second to fourth embodiments of thepresent invention, since there are a plurality of light receivingelements having specific positional information and there are aplurality of dispersed light receiving element arrays comprised ofpluralities of light receiving elements having that specific positionalinformation, when the illuminance of the light source is uneven orspotty or when the glass scale 10 is scratched or dirty, the effect issuffered a bit by all of the light receiving elements of the positionalinformation and averaged out, so it is possible to prevent anydetrimental effect on the measurement precision.

FIG. 21 shows the configuration of a photoelectric transmission typelinear encoder to which fifth to 10th embodiments of the presentinvention are applied and shows one embodiment of the internalconfiguration of the contact type digital displacement meter 40explained in FIG. 1. Reference numeral 10 is a glass scale provided withan optical grid 11, while reference numeral 1 is a light source foremitting parallel light to the glass scale 10. Reference numeral 200A isan aggregate of light receiving elements for receiving light passingthrough the glass scale 10. Reference numeral 22 is a semiconductorintegrated circuit (IC chip) for position processing. Reference numeral21 is a terminal for connecting with a cable 70. The cable 70 suppliespower or transmits signals to a display device or other external device.The aggregate 200A of light receiving elements, a semiconductorintegrated circuit 22, and a terminal 21 are mounted on the board 20.

FIG. 22 shows details of the optical grid 11 and aggregate 200A of lightreceiving elements in the fifth embodiment of the present invention.Twenty light receiving elements 39-1 to 39-20 are arranged in parallelin the direction of movement A-B of the glass scale 10 shown by thearrow A-B. W shows the width of a transparent portion 12 of the opticalgrid 11, while V shows the width of a nontransparent portion 13 of theoptical grid 11. Here, the width W of the transparent portion 12 of theoptical grid 11 and the width V of the nontransparent portion 13 are setto S/2, respectively. If for example the pitch S of the optical grid 11of the glass scale 10 is set to 20 μm, the width W of the transparentportion 12 of the optical grid 11 is 10 μm and the width V of thenontransparent portion of the optical grid 11 is also 10 μm.

The aggregate 200A of the light receiving elements is comprised of aplurality of light receiving elements 39-1 to 39-20. Each lightreceiving element 39 is comprised of a valid light receiving portion 35able to receive light and an invalid light receiving portion 36 unableto receive light. P indicates the width of a light receiving element 39,u indicates the width of the valid light receiving portion 35, and rindicates the width of the invalid light receiving portion. Here, thewidth u of the valid light receiving portion 35 is the same as the widthW of the transparent portion 12 of the optical grid 11, but the width rof the invalid light receiving portion is smaller than the width V ofthe nontransparent portion 13 of the optical grid 11. Therefore, thepitch P of each light receiving element 39 is made smaller than thepitch S of the optical grid 11.

As will be understood from FIG. 22, one group is comprised of 20 lightreceiving elements 39-1 to 39-20 arranged in a direction parallel to thedirection of movement A-B of the glass scale. The light receivingelements 39-1 to 39-20 are all of the same dimensions. Six such groupsare arranged in the direction of movement of the glass scale (FIG. 22shows only part of the six groups). Further, one light receiving element39 is arranged in the direction perpendicular to the direction ofmovement A-B of the glass scale.

The width u of the valid light receiving portion 35 of each lightreceiving element 39 is set to 10 μm in the same way as the width W ofthe transparent portion 12 of the optical grid 11, while the width r ofthe invalid light receiving portion 36 is set to 3 μm or smaller thanthe width V of the nontransparent portion 13 of the optical grid 11.Therefore, the pitch P of each light receiving element 39 is made 13 μmor smaller than the pitch S of the optical grid 11. Therefore, thelength Lx of each light receiving element group in the lateral directionbecomes 260 μm (13 μm×20). Therefore, the length LLx of the aggregate200 of the light receiving elements 39 in the direction of movement ofthe glass scale is 1560 μm (260 μm×6) since there are six lightreceiving element groups. Further, the length LLy of each lightreceiving element array is set to 1600 μm.

FIG. 22 will be used to explain the content of a light receiving elementgroup in detail. A transparent portion 12 of the optical grid 11 of theglass scale and the valid light receiving portion 35 of the lightreceiving element 39-1 in the light receiving element group are made tomatch. By doing this, since N is made a number of 1 to 20 and the lightreceiving element 39-N next to the light receiving element 39-1 has alight receiving element pitch P of 13 μm, by movement of the glass scale10 in the A direction by exactly 13 μm, the transparent portion 12 ofthe optical grid 11 of the glass scale and the valid light receivingportion 35 match. Therefore, this light receiving element 39-N isdesignated as the light receiving element 39-14.

Further, since M is a number from 1 to 20 and the adjoining lightreceiving element 39-M is two pitches away, that element is at aposition 26 μm from the light receiving element 39-1, but the pitch ofthe optical grid 11 of the glass scale 10 is 20 μm, so when the glassscale 10 moves by 6 μm, the transparent portion 12 of the optical grid11 of the glass scale and the valid light receiving portion 35 match.Therefore, this light receiving element 39-M is designated as the lightreceiving element 39-7.

In this way, if Q is made a number of 1 to 20, the number Q of the lightreceiving element 39-Q is increased by 13 at a time starting from 1, andthe number Q of the light receiving element 39-Q is determined by theresult of calculation by a module 20 (provided, however, that Q>0 isreplaced with Q=Q−20), the numbers from Q=1 to 20 all appear in onelight receiving element group. Further, the number Q minus 1 correspondsto the amount of shift from the transparent portion 12 of the opticalgrid 11 of the glass scale, that is, the position shifted in the Adirection of the direction of movement A-B of the glass scale 10.

The least common multiple of the pitch P (=13 μm) of the light receivingelements 39 and the pitch S (=20 μm) of the optical grid 11 is 260 μm.Therefore, it is understood that a light receiving element group 39repeats every 260 μm. That is, it is understood that the head of thenext group also becomes the light receiving element 39-1 and that it isat the same position relative to the optical grid 11 as the head lightreceiving element 39-1 of the previous group.

In this way, it is understood that the light receiving elements havingthe same number Q in the groups have the same amount of shift from thetransparent portions 12 of the optical grid 11 of the glass scale andthat the outputs obtained by movement of the glass scale 10 are also thesame. Therefore, 20 different types of output signals are obtained fromthe light receiving elements 39-1 to 39-20 for the pitch S (=20 μm) ofthe glass scale 10. Further, since the 20 different types of outputsignals are shifted in phase corresponding to 1 μm each, these signalsmay be processed to obtain signals expressing each 1 μm. This processingwill be explained later.

The signals the same as in the fifth embodiment may be prepared in thefashion of FIG. 23. In FIG. 23, when the pitch S of the optical grid 11of the glass scale is 20 μm, the width W of the transparent portion 12of the optical grid 11 is 10 μm, and the width V of the nontransparentportion of the optical grid 11 is also 10 μm, the width u of the validlight receiving portion of a light receiving element 39 becomes 10 μmand the width r of the invalid light receiving portion becomes 10 μm. Inthis way, 80 light receiving elements 39 are arranged parallel to thedirection of movement of the glass scale 10 to form an array. A total of20 arrays the same as this are arranged in the A direction of thedirection of movement of the glass scale 10 shifted by 1 μm increments.By doing this, since the light receiving elements 39 in the arrays areat the same positions relative to the optical grid 11, the outputsaccompanying movement of the glass scale 11 in the arrays are the same.Therefore, 20 different outputs are obtained from each array. These areshifted by phases corresponding to 1 μm, so these signals may beprocessed to obtain signals expressing each 1 μm.

Here, the total area of one valid light receiving portion of a signalobtained by the configuration of FIG. 23 and the total area of one validlight receiving portion of a signal obtained by the fifth embodiment ofthe present invention will be compared. In both cases, the overall sizeof the light receiving elements is set about the same to about 1600μm×1600 μm. The area of the configuration of FIG. 23 is u μm×Ly μm×n(number)=64,000 μm², while the area of fifth embodiment is 10×1600μm×6=96,000 μm. Therefore, according to the present invention, even ifthe overall size of the light receiving elements is the same, 1.5 timesthe output is obtained.

Further, when the illuminance of the light source is uneven or spotty orwhen the glass scale is scratched or dirty, as will be understood from acomparison of FIG. 22 and FIG. 23, since the light receiving elements39-1 of FIG. 22 are arranged dispersed at equal intervals, the effect isresisted. As opposed to this, the light receiving element of the firstarray corresponding to the light receiving element 39-1 of FIG. 23 issusceptible to the effects since there is only one array.

According to the fifth embodiment, since the width of the valid lightreceiving portion of a light receiving element is made to be larger thanthe width of the invalid light receiving portion, the area of the validlight receiving portion of the light receiving element can be increasedat the portion struck by light, greater resistance to noise can beobtained, and a detrimental effect on the measurement precision can beprevented.

Further, since there are a plurality of dispersed light receivingelements having specific positional information and even when theilluminance of the light source is uneven or spotty or the glass scaleis scratched or dirty, the effect is dispersed and averaged out by allthe light receiving elements of the positional information, it ispossible to prevent this from having a detrimental effect on themeasurement precision.

FIG. 24 shows the configuration of a sixth embodiment of the presentinvention. In the sixth embodiment, the positional relationships of thelight source 1, glass scale 10, and board 20 are similar to theconfiguration explained in FIG. 21. In the sixth embodiment, however, asshown in FIG. 24, the configuration of the aggregate 200A of lightreceiving elements differs from the fifth embodiment.

FIG. 24 shows details of the optical grid 11 and the aggregate 200A oflight receiving elements. In the sixth embodiment, 20 light receivingelements 39-1 to 39-20 (in the figure, shown by the numbers 1 to 20)form one group. Each group is comprised of the 20 light receivingelements arranged five in the direction parallel to the direction ofmovement A-B of the glass scale 10 and arranged four in the directionperpendicular to the direction of movement of the glass scale 10. Eacharray is arranged shifted by 1 μm in the A direction of the direction ofmovement of the glass scale 10. If the pitch S of the optical grid 11 ofthe glass scale 10 is set to 20 μm, the width W of the transparentportion 12 of the optical grid 11 is 10 μm and the width V of thenontransparent portion 13 of the optical grid 11 is also 10 μm.

As will be understood from FIG. 24, the light receiving elements 39-1 to39-20 in each group comprised of five light receiving elements 39arranged in the direction of movement A-B of the glass scale 10 and fourin the direction perpendicular to the direction of movement A-B of theglass scale 10, that is, the total 20, are all of the same dimensions.In the sixth embodiment, 27 such groups are arranged in the direction ofmovement of the glass scale 10. The width u of the valid light receivingportion 35 of each light receiving element 39 is set to 10 μm in thesame way as the width W of the transparent portion 12 of the opticalgrid 11, while the width r of the invalid light receiving portion 36 isset to 2 μm or smaller than the width V of the nontransparent portion 13of the optical grid 11. Therefore, the pitch P of each light receivingelement 39 is made 12 μm or smaller than the pitch S of the optical grid11. Therefore, the length Lx of each light receiving element group inthe lateral direction becomes 60 μm (=12 μm×5). Therefore, the lengthLLx of the aggregate 200A of light receiving elements 39 in thedirection of movement of the glass scale 10 becomes 1623 μm (=60 μm×27+3μm) since there are 27 light receiving element groups. Further, thelength Ly of each light receiving element array is set to 400 μm, so thelength LLy in the direction perpendicular to the direction of movementof the glass scale 10 is set to 1600 μm.

FIG. 24 will be used to explain the content of a light receiving elementgroup in detail. A transparent portion 12 of the optical grid 11 of theglass scale and the valid light receiving portion 35 of the lightreceiving element 39-1 in the light receiving element group are made tomatch. By doing this, since the light receiving element 39-N of thefirst array next to the light receiving element 39-1 has a lightreceiving element pitch P of 12 μm, when the glass scale 10 moves in theA direction by exactly 12 μm, the transparent portion 12 of the opticalgrid 11 of the glass scale and the valid light receiving portion 35match. Therefore, this light receiving element 39-N is designated as thelight receiving element 39-13. Further, since the adjoining lightreceiving element 39-M is two pitches away, that element is at aposition 24 μm from the light receiving element 39-1, but the pitch ofthe optical grid 11 of the glass scale 10 is 20 μm, so when the glassscale 10 moves by 4 μm, the transparent portion 12 of the optical grid11 of the glass scale and the valid light receiving portion 35 match.Therefore, this light receiving element is designated as the lightreceiving element 39-5.

In this way, if the number Q of the light receiving element 39-Q isincreased by 12 at a time starting from 1 and the number Q of the lightreceiving element 39-Q is determined by the result of calculation by amodule 20 (provided, however, that Q>0 is replaced with Q=Q−20), thereare five Qs, that is, 1, 13, 5, 17, and 9.

The head light receiving element 39-Q of the second array is shifted by1 μm with respect to the light receiving element 39-1, that is, thetransparent portion 12 of the optical grid 11 and the valid lightreceiving portion 35 are shifted by 1 μm, so the light receiving element39-Q becomes the light receiving element 39-2. This array starts fromQ=2. If Q is increased by 12 at a time and the result of calculation bythe module 20 is made the number, five numbers are obtained for Q, thatis, 2, 14, 6, 18, and 10.

The third array and the fourth array similarly start from Q=3 or Q=4. Ifadding 12 at a time to Q, the result calculated at the module 20(provided, however, that Q>0 is replaced by Q=Q−20) is made the numberand a Q of 3, 15, 7, 19, and 11 and a Q of 4, 16, 8, 20, and 12 areobtained. Therefore, the numbers from Q=1 to 20 all appear in each lightreceiving element group. Further, the number Q minus 1 corresponds tothe amount of shift from the transparent portions 12 of the optical grid11 of the glass scale 10, that is, the position shifted in the Adirection of the direction of movement A-B of the glass scale 10.

The least common multiple of the 12 μm of the pitch P of the lightreceiving elements 39 and the 20 μm of the pitch S of the optical grid11 is 60 μm. Therefore, it is understood that this group repeats every60 μm. That is, it is understood that the head of the next group alsobecomes the light receiving element 39-1 and that it is at the sameposition relative to the optical grid 11 as the head light receivingelement 39-1 of the previous group.

In this way, it is understood that the light receiving elements havingthe same number Q in a group have the same amount of shift from thetransparent portions 12 of the optical grid 11 of the glass scale andthat the outputs obtained by movement of the glass scale 10 are also thesame. Therefore, 20 different types of output signals are obtained fromthe light receiving elements 39-1 to 39-20 for the 20 μm of the pitch Sof the glass scale 10. Since the output signals are shifted by 1 μmincrements, these signals may be processed to obtain signals expressingeach 1 μm. This processing will be explained later.

Here, the total area of one valid light receiving portion of a signalobtained by the configuration of FIG. 23 and the total area of one validlight receiving portion of a signal obtained by the sixth embodiment ofthe present invention will be compared. In both cases, the overall sizeof the light receiving elements is set about the same to about 1600μm×1600 μm. The area of the configuration of FIG. 23 is u μm×Ly μm×n(number)=64,000 μm², while the area of sixth embodiment is 10×400μm×27=108,000 μm². Therefore, according to the present invention, evenif the overall size of the light receiving elements is the same, 1.7times the output is obtained.

In the sixth embodiment as well, in the same way as the fifthembodiment, since the light receiving elements having the samepositional information are arranged dispersed and a large lightreceiving area is obtained, a large output signal is obtained and, evenwhen the illuminance of the light source is uneven or spotty or when theglass scale is scratched or dirty, the effect is dispersed and averagedout by all of the light receiving elements of the positionalinformation, so it is possible to prevent this from having a detrimentaleffect on the measurement precision.

FIG. 25 shows details of the optical grid 11 and the aggregate 200A ofthe light receiving elements in a seventh embodiment of the presentinvention. The positional relationships of the light source 1, glassscale 10, and board 20 are similar to those of the configurationexplained in FIG. 21. In the seventh embodiment, however, as shown inFIG. 25, the configuration of the aggregate 200A of the light receivingelements differs from that of the fifth embodiment.

FIG. 25 shows details of the optical grid 11 and the aggregate 200A ofthe light receiving elements. In the seventh embodiment, 20 lightreceiving elements 39-1 to 39-20 (in the figure, shown by the numbers 1to 20) form one group. Each group is comprised of a total of 10elements×2 arrays, that is, 10 elements in the direction of movement A-Bof the glass scale 10 and two arrays in the direction perpendicular tothe direction of movement of the glass scale 10. Each array is arrangedparallel to the direction of movement A-B of the glass scale 10. Thegroup of the second array is arranged shifted by 1 μm in the A directionof the direction of movement of the glass scale 10. If the pitch S ofthe optical grid 11 of the glass scale 10 is set to 20 μm, the width Wof the transparent portion 12 of the optical grid 11 is 10 μm and thewidth V of the nontransparent portion 13 of the optical grid 11 is also10 μm.

As will be understood from FIG. 25, each group is comprised of 10 lightreceiving elements in the direction of movement A-B of the glass scale10 and two arrays in the direction perpendicular to the direction ofmovement A-B of the glass scale 10, that is, the total 20. The lightreceiving elements 39-1 to 39-20 are all of the same dimensions. In theseventh embodiment, 11 such groups are arranged in the direction ofmovement of the glass scale 10. The width u of the valid light receivingportion 35 of each light receiving element 39 is set to 10 μm in thesame way as the width W of the transparent portion 12 of the opticalgrid 11, while the width r of the invalid light receiving portion 36 isset to 4 μm or smaller than the width V of the nontransparent portion 13of the optical grid 11. Therefore, the pitch P of each light receivingelement 39 is made 14 μm or smaller than the pitch S of the optical grid11. Therefore, the length Lx of each light receiving element group inthe direction of movement of the glass scale 10 becomes 140 μm (=14μm×10). Therefore, the length LLx of the aggregate 200A of lightreceiving elements 39 in the direction of movement of the glass scale 10becomes 1541 μm (=140 μm×11+1 μm) since there are 11 light receivingelement groups. Further, the length Ly of each light receiving elementarray is set to 800 μm, so the length LLy in the direction perpendicularto the direction of movement of the glass scale 10 is 1600 μm.

FIG. 25 will be used to explain the content of a light receiving elementgroup in detail. A transparent portion 12 of the optical grid 11 of theglass scale and the valid light receiving portion 35 of the lightreceiving element 39-1 of the first array in the light receiving elementgroup are made to match. By doing this, since the light receivingelement 39-N of the first array next to the light receiving element 39-1has a light receiving element pitch P of 14 μm, when the glass scale 10moves in the A direction by exactly 14 μm, the transparent portion 12 ofthe optical grid 11 of the glass scale and the valid light receivingportion 35 match. Therefore, this light receiving element 39-N isdesignated as the light receiving element 39-15. Further, since theadjoining light receiving element 39-M is two pitches away, that elementis at a position 28 μm from the light receiving element 39-1, but thepitch of the optical grid 11 of the glass scale 10 is 20 μm, so when theglass scale 10 moves by 8 μm, the transparent portion 12 of the opticalgrid 11 of the glass scale and the valid light receiving portion 35match. Therefore, this light receiving element is designated as thelight receiving element 39-9. In this way, if the number Q of the lightreceiving element 39-Q is increased by 14 at a time starting from 1 andthe number Q of the light receiving element 39-Q is determined by theresult of calculation by the module 20, there are 10 Qs, that is, 1, 15,9, 3, 17, 11, 5, 19, 13, and 7.

The head light receiving element 39-Q of the second array is shifted by1 μm with respect to the light receiving element 39-1, that is, thetransparent portion 12 of the optical grid 11 and the valid lightreceiving portion 35 are shifted by 1 μm, so the light receiving element39-Q becomes the light receiving element 39-2. This array starts fromQ=2. If Q is increased by 14 at a time and the result of calculation bythe module 20 (provided, however, that Q>0 is replaced by Q=Q−20), 10Qs, that is, 2, 16, 10, 4, 18, 12, 6, 20, 14, and 8, are obtained.Therefore, the numbers from Q=1 to 20 all appear in each light receivingelement group. Further, the number Q minus 1 corresponds to the amountof shift from the transparent portions 12 of the optical grid 11 of theglass scale 10, that is, the position shifted in the A direction of thedirection of movement A-B of the glass scale 10.

The least common multiple of the 14 μm of the pitch P of the lightreceiving elements 39 and the 20 μm of the pitch S of the optical grid11 is 140 μm. Therefore, it is understood that this group repeats every140 μm. That is, it is understood that the head of the next group alsobecomes the light receiving element 39-1 and that it is at the sameposition relative to the optical grid 11 as the head light receivingelement 39-1 of the previous group.

In this way, it is understood that the light receiving elements havingthe same number Q among the groups have the same amount of shift fromthe transparent portions 12 of the optical grid 11 of the glass scale 10and that the outputs obtained by movement of the glass scale 10 are alsothe same. Therefore, 20 different types of output signals are obtainedfrom the light receiving elements 39-1 to 39-20 for the 20 μm of thepitch S of the glass scale 10. Since the output signals are shifted by 1μm increments, these signals may be processed to obtain signalsexpressing each 1 μm. This processing will be explained later.

The total area of one valid light receiving portion of a signal obtainedin the above way and the total area of one valid light receiving portionof a signal obtained in FIG. 23 will be compared. In both cases, theoverall size of the light receiving elements is set about the same toabout 1600 μm×1600 μm. The area of the configuration of FIG. 23 is uμm×Ly μm×n (number)=64,000 μm², while the area of the seventh embodimentis 10×800 μm×11=88,000 μm². Therefore, according to the presentinvention, even if the overall size of the light receiving elements isthe same, about 1.4 times the output is obtained.

In the seventh embodiment as well, in the same way as the fifthembodiment, since the light receiving elements having the samepositional information are arranged dispersed and a large lightreceiving area is obtained, a large output signal is obtained and, evenwhen the illuminance of the light source is uneven or spotty or when theglass scale is scratched or dirty, the effect is dispersed and averagedout by all of the light receiving elements of the positionalinformation, so it is possible to prevent this from having a detrimentaleffect on the measurement precision.

FIG. 26 shows the configuration of an eighth embodiment of the presentinvention. In the eighth embodiment as well, the positionalrelationships of the light source 1, glass scale 10, and board 20 aresimilar to the configuration explained in FIG. 21. In the eighthembodiment, however, as shown in FIG. 26, the configuration of theaggregate 200A of light receiving elements differs from the fifthembodiment.

FIG. 26 shows details of the optical grid 11 and the aggregate 200A oflight receiving elements. In the eighth embodiment, 20 light receivingelements 39-1 to 39-20 (in the figure, shown by the numbers 1 to 20)form one group. Each group is comprised of the 20 light receivingelements arranged four in the direction parallel to the direction ofmovement A-B of the glass scale 10 and arranged five in the directionperpendicular to the direction of movement of the glass scale 10. Eacharray from the second array on is arranged shifted by 1 μm increments inthe A direction of the direction of movement of the glass scale 10.

As will be understood from FIG. 26, each group is comprised of fourlight receiving elements 39 in the direction of movement A-B of theglass scale 10 and five arrays in the direction perpendicular to thedirection of movement, that is, the total 20. The light receivingelements 39-1 to 39-20 are all of the same dimensions. In the eighthembodiment, 27 such groups are arranged in the direction of movement ofthe glass scale 10. The width u of the valid light receiving portion 35of each light receiving element 39 is set to 10 μm in the same way asthe width W of the transparent portion 12 of the optical grid 11, whilethe width r of the invalid light receiving portion 36 is set to 5 μm orsmaller than the width V of the nontransparent portion 13 of the opticalgrid 11. Therefore, the pitch P of each light receiving element 39 ismade 15 μm or smaller than the pitch S of the optical grid 11.Therefore, the length Lx of each light receiving element group in thelateral direction of movement of the glass scale 10 becomes 60 μm (=15μm×5). Therefore, the length LLx of the aggregate 200A of lightreceiving elements 39 in the direction of movement of the glass scale 10becomes 1624 μm (=60 μm×27+4 μm) since there are 27 light receivingelement groups. Further, the length Ly of each light receiving elementarray is set to 320 μm, so the length LLy in the direction perpendicularto the direction of movement of the glass scale 10 is 1600 μm.

The eighth embodiment clearly also has the same effects as the previousembodiments. Note that the total area of one valid light receivingportion of a signal obtained in the eighth embodiment and the total areaof one valid light receiving portion of a signal obtained in FIG. 23will be compared. In both cases, the overall size of the light receivingelements is set about the same to about 1600 μm×1600 μm. The area of theconfiguration of FIG. 23 is 64,000 μm², while the area of the eighthembodiment is 10 μm×320 μm×27=86,400 μm². Therefore, according to thepresent invention, even if the overall size of the light receivingelements is the same, about 1.35 times the output is obtained.

Each array of the eighth embodiment is structured very similar to thethird prior art explained above. That is, for a pitch S (=20 μm) of theoptical grid 11, the pitch P of each light receiving element is set to3×S/4=15 μm, the width u of the valid light receiving portion 35 toS/2=10 μm, and the width r of the invalid light receiving portion toS/4=5 μm.

In the prior art, however, there was only one of the arrays of the eightembodiment. That single array was broken down to 20 μm for themeasurement, so the measurement precision was poor. In the eighthembodiment, however, five of these arrays are provided and the arraysare shifted by 1 μm increments, so 20 outputs are obtained by a singlepitch of 20 μm in the measurement and therefore the precision is high.

Next, a ninth embodiment of the present invention will be explainedusing FIG. 27. In the ninth embodiment, the positional relationships ofthe light source 1, glass scale 10, and board 20 are similar to those ofthe configuration explained in FIG. 21. In the ninth embodiment,however, as shown in FIG. 27, the configuration of the aggregate 200A oflight receiving elements differs from that of the sixth embodiment.

In the sixth embodiment explained in FIG. 24, the size of the lightreceiving elements 39 was set to a width u of the valid light receivingportions 35 of 10 μm, a width r of the invalid light receiving portionsof 2 μm, and a length Ly in the longitudinal direction of 400 μm.Further, 20 light receiving elements arranged in four arrays of lightreceiving elements 39 shifted 1 μm each in the direction of movement ofthe glass scale formed one group. Twenty-seven of these groups werearranged in the direction of movement of the glass scale to form asingle light receiving element group. Therefore, in the sixthembodiment, the length Ly of each group in the direction perpendicularto the direction of movement of the glass scale was 1600 μm, while thetotal length LLx of the aggregate 200A of the light receiving elementsin the direction of movement of the glass scale was 1623 μm.

On the other hand, in the ninth embodiment shown in FIG. 27, the size ofeach light receiving element 39 is a width u of the valid lightreceiving portion 35 of 10 μm and a width r of the invalid lightreceiving portion of 2 μm, both the same, but the width Ly in thedirection perpendicular to the direction of movement of the glass scaleis set to 200 μm (half of the value of the sixth embodiment). Therefore,the length of each group in the direction perpendicular to the directionof movement of the glass scale is 800 μm. In the ninth embodiment, 13 ofsuch groups are arranged in the direction of movement of the glass scaleto form a light receiving element group 201.

Further, a light receiving element group of the same configuration asthe light receiving element group 201 is arranged adjoining the lightreceiving element group 201 in the direction perpendicular to thedirection of movement of the glass scale to form the light receivingelement group 202. As a result, the total length of the aggregate 200Aof light receiving element groups in the direction perpendicular to thedirection of movement of the glass scale becomes 1600 μm. At that time,as shown in FIG. 27, the head light receiving element of the lightreceiving element group 202 is shifted by 1 μm in the A direction of thedirection of movement of the glass scale 10 with respect to the lightreceiving element group 201.

If arranged in this way, it is understood that the head of the lightreceiving element group 202 is positioned shifted by 1 μm from atransparent portion 12 of the optical grid 11, is positioned the samerelatively as the light receiving element 39-2 of the light receivingelement group 202, and emits the same positional signal due to movementof the light receiving element group 11. Therefore, if numbers areassigned from the positions of the light receiving elements 39 of thelight receiving element group 202 relative to the transparent portions12 of the optical grid 11, the light receiving elements 39-1 to 39-20are assigned as numbers 1 to 20 in the light receiving element group 202such as shown in FIG. 27.

Further, the light receiving element groups 203 and 204 are arranged atpositions adjoining the light receiving element groups 201 and 202shifted by 2 μm increments in the A direction of the direction ofmovement of the glass scale 10. The light receiving element group 204 isshifted 1 μm in the A direction of the direction of movement of theglass scale 10 with respect to the light receiving element group 203. Byarranging the groups in this way, it is understood that the head of thelight receiving element group 203 is positioned shifted 2 μm withrespect to a transparent portion 12 of the optical grid 11, ispositioned the same relatively as with the light receiving element 39-3of the light receiving element group 201, and emits the same positionalsignal. Therefore, if numbers are assigned from the positions of thelight receiving elements 39 of the light receiving element group 203relative to the transparent portions 12 of the optical grid 11, thelight receiving elements 39-1 to 39-20 are assigned as the numbers 1 to20 in the light receiving element group 203 as shown in FIG. 27.

Similarly, it is understood that the head of the light receiving elementgroup 204 is positioned shifted 3 μm with respect to the transparentportion 12 of the optical grid 11, is positioned the same relatively asthe light receiving element 39-4 of the light receiving element group201, and emits the same positional signal. Therefore, if numbers areassigned from the positions of the light receiving elements 39 of thelight receiving element group 204 relative to the transparent portions12 of the optical grid 11, the light receiving elements 39-1 to 39-20are assigned as the numbers 1 to 20 in the light receiving element group204 as shown in FIG. 27.

If arranged in this way, the size of the aggregate 200A of the lightreceiving element groups in the ninth embodiment becomes a length LLx inthe direction of movement of the glass scale of 1626 μm and a length LLyin the direction perpendicular to the direction of movement of the glassscale of 1600 μm. In this way, in the ninth embodiment, the size becomessubstantially the same as in the sixth embodiment (length LLx indirection of movement of glass scale is just 3 μm larger).

If arranging the groups as in the ninth embodiment, however, forexample, if taking note of the light receiving elements 39-1 arranged atthe same positions relatively and emitting the same signal for movementof the glass scale 10, the overall light receiving area is the same. InFIG. 24, what was divided in the first array is distributed among thesecond, third, and fourth arrays as well so it is understood that theyare distributed more broadly.

That is, the configuration of the ninth embodiment is equivalent to theaggregate 200A of light receiving element groups shown in FIG. 21comprised of the four light receiving element groups 201 to 204 like thelight receiving element group 200 explained in FIG. 12. Therefore, inthis embodiment as well, it is understood that an even greater effect isobtained.

In the ninth embodiment, the explanation was given using the arrangementof the light receiving element arrays shown in FIG. 24 for the groups oflight receiving elements in the four light receiving element groups 201to 204, but it is clear that similar effects are obtained even if usingthe groups explained in FIG. 25 and FIG. 26 for the groups of lightreceiving elements in the four light receiving element groups 201 to204.

Finally, a 10th embodiment of the present invention will be explainedusing FIG. 28. In the 10th embodiment, the positional relationships ofthe light source, glass scale 10, and board 20 are similar to those inthe configuration explained in FIG. 21. In the 10th embodiment, however,as shown in FIG. 28, the configuration of the aggregate 200A of lightreceiving elements differs from those of the previous embodiments.

In the 10th embodiment, the pitch S of the optical grid 11 of the glassscale 10 is set to 8 μm, the width W of the transparent portion 12 ofthe optical grid 11 is set to 4 μm, while the width V of thenontransparent portion 13 of the optical grid 11 is set to 4 μm. Thewidth u of the valid light receiving portion 35 of each light receivingelement 39 is set to 4 μm in the same way as the width W of thetransparent portion 12 of the optical grid 11, while the width r of theinvalid light receiving portion 36 is set to 3 μm or smaller than thewidth V of the nontransparent portion 13 of the optical grid 11.

The aggregate 200A of the light receiving elements is comprised of aplurality of light receiving elements 39-1 to 39-8. The eight lightreceiving elements 39-1 to 39-8 arranged in a direction parallel to thedirection of movement A-B of the glass scale form one group. The lightreceiving elements 39-1 to 39-8 all have the same dimensions.Twenty-eight of such groups are arranged in the direction of movement ofthe glass scale (FIG. 28 shows only part of them). Further, one lightreceiving element 39 is arranged in the direction perpendicular to thedirection of movement A-B of the glass scale.

The length Lx of each light receiving element group in the lateraldirection becomes 56 μm (=7 m×8). Therefore, the length LLx of theaggregate 200 of light receiving elements 39 in the direction ofmovement of the glass scale becomes 1568 μm (=56 μm×28) since there are28 light receiving element groups. Further, the length LLy of each lightreceiving element array is set to 1600 μm.

A transparent portion 12 of the optical grid 11 of the glass scale andthe valid light receiving portion 35 of the light receiving element 39-1in the light receiving element group are made to match. By doing this,since the light receiving element 39-N next to the light receivingelement 39-1 has a light receiving element pitch P of 7 μm, when theglass scale 10 moves in the A direction by exactly 7 μm, the transparentportion 12 of the optical grid 11 of the glass scale and the valid lightreceiving portion 35 match. Therefore, this light receiving element 39-Nis designated as the light receiving element 39-8. Further, since theadjoining light receiving element 39-M is two pitches away, that elementis at a position 14 μm from the light receiving element 39-1, but thepitch of the optical grid 11 of the glass scale 10 is 8 μm, so when theglass scale 10 moves by 6 μm, the transparent portion 12 of the opticalgrid 11 of the glass scale and the valid light receiving portion 35match. Therefore, this light receiving element 39-M is designated as thelight receiving element 39-7.

In this way, if the number Q of the light receiving element 39-Q isincreased by 7 at a time starting from 1 and the number Q of the lightreceiving element 39-Q is determined by the result of calculation by amodule 8 (provided, however, that Q>8 is replaced with Q=Q−8), thenumbers from Q=1 to 8 all appear in each group of the light receivingelements as shown in FIG. 28. Further, the number Q minus 1 correspondsto the amount of shift from the transparent portions 12 of the opticalgrid 11 of the glass scale 10, that is, the position shifted in the Adirection of the direction of movement A-B of the glass scale 10.

The least common multiple of the pitch P (=7 μm) of the light receivingelements 39 and the pitch S (=8 μm) of the optical grid 11 is 56 μm.Therefore, it is understood that this group of the light receivingelements 39 repeats every 56 μm. That is, it is understood that the headof the next group also becomes the light receiving element 39-1 and thatit is at the same position relative to the optical grid 11 as the headlight receiving element 39-1 of the previous group.

In this way, it is understood that the light receiving elements havingthe same number Q in the groups have the same amount of shift from thetransparent portions 12 of the optical grid 11 of the glass scale andthat the outputs obtained by movement of the glass scale 10 are also thesame. Therefore, eight different types of output signals are obtainedfrom the light receiving elements 39-1 to 39-8 for the pitch S (=8 μm)of the glass scale 10. Since these eight different types of outputsignals are shifted in phase corresponding to 1 μm each, these signalsmay be processed to obtain signals expressing each 1 μm. This processingwill be explained later.

In this way, in the 10th embodiment, similar effects as in the fifthembodiment are obtained. Since it is possible to arrange 28 groups inthe direction of movement of the glass scale, the light receiving areabecomes 1.12 times greater and a sufficiently dispersed arrangement isobtained. In the 10th embodiment, however, since the pitch p of theoptical grid 11 is 8 μm, eight signals for each 1 μm are obtained. Theprocessing will be explained using FIG. 17.

The flow of the signals will be explained using FIG. 17 and taking as anexample the light receiving element 39-1. Assume that the glass scale 10and the light receiving element 39-1 are in the positional relationshipshown in FIG. 28. That is, assume that the transparent portions 12 ofthe glass scale 10 and the valid light receiving portions 35 of thelight receiving elements 39 match. At this time, the signals obtainedfrom the light receiving elements 39 become maximum. The signal obtainedby adding the signals from all of the light receiving elements 39-1 alsobecomes maximum. When the glass scale 10 moves in the direction ofmovement A, the nontransparent portions 13 of the glass scale 10gradually cover the valid light receiving portions 35 of the lightreceiving elements 39, so the outputs become smaller. When the glassscale 10 moves by exactly ¼ of the pitch S, the outputs become ½ of themaximum output, while when it moves by exactly ½ of the pitch S, theportions are completely covered and the outputs become the minimumoutput. When the glass scale 10 moves further and moves by ¾ of thepitch S, the outputs return to ½ of the maximum output. When moving byexactly 1 pitch S, the maximum outputs are again obtained.

The same is true for the other light receiving elements, but since thelight receiving element 39-2 is positioned shifted 1 μm with respect tothe light receiving element 39-1, the output become maximum 1 μm delayedwith respect to the light receiving element 39-1. In addition, theoutputs of the light receiving elements 39-3 to 39-8 become maximumshifted 1 μm from each other. This relationship is shown by the signalsI31 to I38 in FIG. 17. In the figure, the signal I31 is the outputsignal of the light receiving element 39-1, while the signals I32 to I38correspond to the signals from the light receiving elements 39-2 to39-8.

If converting the signals to digital values using a comparator having athreshold value of (maximum output−minimum output)/2, the results arethe digital signals J31 to J38 in FIG. 17. Here, the signal J31 is thesignal I31 converted to a digital value and inverts at (maximumoutput−minimum output)/2. The signals J32 to J38 correspond to thesignals I32 to 138.

Further, the digital signals J31 to J38 are converted to two signals KAand KB comprised of

A=J31·J37+J33·J35

B=J32·J38+J34·J36

by a logical operation circuit. The timings of the rising edges andtrailing edges of the signals KA and KB are shown in FIG. 17. As will beunderstood from FIG. 17, one cycle of the signal I31 is equal to thepitch S, that is, 8 μm, of the glass scale, so the distance from therising edge or the trailing edge of the signal KA to the trailing edgeor rising edge of the signal KB becomes exactly 1 μm. If counting thenumber of the rising edges or trailing edges of the signals KA and KB,the result is eight per cycle. By displaying these, it is possible touse this as a measuring device. Further, for discriminating thedirection of movement of the glass scale 10, if taking note of therising edge of the signal KB, when the direction of movement is A, thesignal KA becomes “1”, while when the direction of movement is B, thesignal KA becomes “0”, so discrimination is possible.

Here, the explanation was given with reference to a pitch P of theoptical grid 11 in the 10th embodiment of 8 μm, but it is clear that asignal is obtained for each 1 μm by similar processing even in the caseof a pitch P of the optical grid 11 explained in the fifth embodiment toninth embodiment of 20 μm.

As explained above, according to the fifth to 10th embodiments, sincethe width of the valid light receiving portion of each light receivingelement is larger than the width of the invalid light receiving portion,the area of the valid light receiving portion of the light receivingelement at the portion struck by light can be made larger, resistance isgiven against noise, and a detrimental effect on the measurementprecision can be prevented.

Further, since there are a plurality of light receiving elements havingspecific positional information or there are a plurality of lightreceiving element arrays comprised of pluralities of light receivingelements having that specific positional information, and the pluralityof light receiving element arrays having that specific positionalinformation are dispersed at a plurality of locations, even when theilluminance of the light source is uneven or spotty or when the glassscale is scratched or dirty, the effect is suffered a bit by all of thelight receiving elements of the positional information and averaged out,so it is possible to prevent any detrimental effect on the measurementprecision.

What is claimed is:
 1. An optical displacement measurement apparatuscomprising a displaceable first member having an optical grid of scalepitch D, a light source for emitting light of a wavelength λ to saidfirst member, and a light receiving element unit for receiving lightpassing through said first member, wherein a distance between said firstmember and said light receiving element unit is set to (2×D²)/2λ andsaid light receiving element unit is comprised of light receivingelement groups.
 2. An optical displacement measurement apparatus servingas a photoelectric transmission type linear encoder comprising a lightsource for emitting light of a wavelength λ, a first member comprised ofa moving scale having a grid pitch D, and a light receiving elementunit, wherein a distance between the first member and the lightreceiving element unit is set to (2×D²)/2λ.
 3. An optical displacementmeasurement apparatus as set forth in claim 1 or 2, wherein said lightsource is comprised of an LED and a condenser lens and said lightreceiving element unit is a photodiode masked at the same pitch as saidfirst member.
 4. An optical displacement measurement apparatus as setforth in claim 1 or 2, wherein said light source is comprised of an LEDand a condenser lens and said light receiving element unit is comprisedof a photodiode divided into two, is masked by the same pitch and linewidth as said first member, and has the divided portions arrangedshifted by ¼ pitch from each other.
 5. An optical displacementmeasurement apparatus as set forth in claim 1 or 2, wherein said lightreceiving element unit is comprised of two CCDs and the CCDs arearranged shifted by ¼ pitch of said first member.